1. Field of the Invention
This invention relates generally to guitars.
2. Prior Art
An acoustic guitar has a long neck attached to one end of a hollow wooden body. Nylon or steel strings are strung under great tension between the top of the neck and an opposite end of the body. The strings gradually range from thick bass strings toward the bottom of the guitar to thin treble strings toward the top of the guitar. The bass strings are under greater tension than the treble strings. The body is comprised of a front soundboard connected to a backboard by a curved side wall. The center of the soundboard is pierced by a sound hole. The soundboard is made relatively thin to vibrate in response to the vibrations of the strings to amplify the sound. Prior art soundboards generally range from about 3/32" (2.4 mm) thick to 1/8" (3.2 mm) thick.
The soundboard is reinforced by internal braces attached to its inner side to prevent it from warping and caving in under the tension of the strings. Although the braces must be stiff enough to provide support, they must still allow the soundboard to vibrate. As disclosed in Classical Guitar Construction, a book published by The Bold Strummer, Ltd., the numerous bracing designs that have been tried testify to the great difficulty in achieving a good balance between these opposing requirements. The most common braces are each attached to the soundboard along its entire length. Greater support to a thin soundboard is provided by such an arrangement. A thin soundboard must have an even wood grain across its entire surface to provide even sound qualities across its tonal range. The requirement for good quality wood with an even grain structure makes a good quality thin soundboard very expensive. Nevertheless, a good quality soundboard has a limited useful life due to its thinness.
A less common bracing arrangement disclosed on page 16 of Classical Guitar Construction includes a transverse brace with two short arches, so that the brace is attached to the soundboard at its ends, and also along a substantial length of its middle portion. The support provided by this brace is substantially the same as that of more conventional braces.
The guitars disclosed in U.S. Pat. No. 5,461,958 to Dresdener et al. and U.S. Pat. No. 3,685,385 to Rendell also include internal braces that are each attached to the soundboard along its entire length.
All prior art braces are each of the same thickness along its entire length to provide even support across the soundboard. However, since the bass and treble strings are under different tension, prior art braces provide too much support for the treble side, so that uneven tones are produced.